This invention relates to a sunscreening agent capable of protecting the skin against sunburn upon exposure to ultraviolet radiation in the 2950 to 3150 angstrom unit range, to compositions containing such a sunscreen agent, and to the method of protecting the human skin against burning upon exposure to sunlight.
It is well known that the burning (erythema) of the skin which follows excessive exposure to sunlight is caused by ultraviolet rays in the wavelength region between 2950 and 3150 angstrom units (A.), while the cosmetically desirable effect of tanning of the skin is due to rays in the wavelength region between about 3150 to 3650 A. Accordingly, a large number of commercial sunscreen compositions are presently marketed in the form of lotions, oils, creams, or the like, which are intended to protect the user against sunburn while permitting tanning to occur. Such commercial compositions contain one or more sunscreening agents which are intended to absorb a substantial portion of the rays in the burning region (2950 to 3150 A.) while allowing transmission of a substantial portion of the rays in the region above 3150 A. Numerous commercially prepared chemical compounds, such as salicylates, para-aminobenzoates, napthoates, and the like have been disclosed in the prior art as having the property of absorbing ultraviolet rays in the 2950-3150 A. region and therefore capable of being used in such commercial compositions.
However, the ability to absorb rays in the burning region is but one of the many properties a material must possess in order to be suitable for use as a sunscreening agent in commercial compositions. The most essential property is a very high absorption of burning rays so that only very small concentrations of the sunscreen agent need be used in the commercial composition. The agent must also have a high ratio of transmittancy of rays in the tanning region to the transmittancy of rays in the burning region so that tanning may occur. In addition, the material must be stable in sunlight, be capable of absorbing burning rays for a period of several hours, be nontoxic, non-irritating and not have any adverse effects on the skin. Moreover, the sunscreen agent should be soluble in a diversity of solvents, including both oils and non-oily substances, so that it can be readily incorporated in the vehicle or base of the commercial composition, but should have a low degree of solubility in water.
Commercially prepared chemical compounds presently being used as sunscreen agents in commercial compositions generally lack one or more of these properties. For example, salicylates have a low absorptive capacity which therefore requires the use of high concentrations of the order of 10% or more in order to be effective. Para-aminobenzoates have the disadvantage of having an analgesic effect on the skin. Naphthoates have poor solubility characteristics and relatively low absorptivities. Moreover, a substantial number of persons do not desire to use compositions containing commercially prepared chemical compounds and would prefer to use sunscreening compositions containing naturally occurring substances. While some naturally occurring substances such as lanolin, peanut oil, sesame oil and petrolatum have been disclosed as being suitable for use as sunscreening agents, such naturally occurring materials which have been suggested heretofor are generally not as effective as chemical sunscreening agents in absorbing high amounts of ultraviolet rays in the burning region.